This invention relates to motor control systems and, more particularly, to a motor control system utilizing a low cost switched controller for providing operator initiated control signals.
Conventional operator influenced motor control systems typically utilize an operator settable resistance for controlling motor speed. For example, the foot controller for a sewing machine motor speed control system typically utilizes either a carbon pile type resistor in order to control the current to the motor or a slide potentiometer to control the voltage speed reference in an SCR closed loop servo system. In either case, operator influence of the speed is effected by the operator varying the depression of the foot controller.
In recent years, motor driven appliances such as, for example, sewing machines, have become increasingly sophisticated, to the point where they may be controlled by microcomputers. With such a device, the full processing capability of the microcomputer is very rarely reached. Accordingly, it would be desirable to utilize the microcomputer for controlling additional functions of the appliance to thereby eliminate a certain amount of hardware and circuitry, resulting in lower costs. The motor speed control function of the appliance is one such candidate for incorporation by the microcomputer operation. It is therefore an object of the present invention to provide a motor control arrangement which is compatible with a microcomputer controlled appliance.
In order to provide the speed control function with a computer controlled system, the operator influenced controller information must be made compatible with the digital nature of the computer. This may be accomplished in a conventional manner by buffering the resistive signal from a conventional controller with a converter such as an analog-to-digital or an analog-to-frequency type. While this is effective, it also increases the cost of the system by adding the cost of the converter to the cost of the conventional controller. It is therefore another object of this invention to provide an improved controller which is directly compatible with computer operation.
In certain applications, such as for example in a sewing machine, the actual speed per se is not important, but rather the controlling element is how the operator perceives the speed. It is therefore a further object of this invention to provide an improved controller compatible with operator perception of speed.